Georgia researcher to track pigweed resistance trait

Even though springtime tree pollen covers much of Georgia now, Lynn Sosnoskie plans to track a different kind of pollen this summer, one that has the potential to spread the worst thing to hit Georgia cotton in decades.

Sosnoskie, a post doctoral research associate with the University of Georgia College of Agricultural and Environmental Sciences, will run experiments in cotton fields, greenhouses and laboratories to learn more about the pollen released by Palmer amaranth, a nasty plant commonly called pigweed.

She wants to know how much pollen a pigweed plant produces, when it produces it, what it looks like, how far the pollen flies, how long it is viable and how weather affects it. The cotton industry wants answers, because inside some of those tiny pollen grains is a genetic trait that could force Georgia farmers to change the way they grow cotton, or force them to stop growing it altogether.

“There isn’t much literature out there on anything like this. We’re pretty much making it as we go,” she said.

Farmers in some areas can no longer kill pigweed with glyphosate, a popular herbicide sold under the brand name Roundup. It’s the one weed they didn’t want to develop resistance to glyphosate. It can grow several inches per day and be the size of a small tree in a few months. It steals nutrients away from cotton plants and can clog cotton harvesters.

In 1997, farmers started planting cotton that was developed to stay healthy when sprayed with Roundup. They could spray the herbicide over-the-top of this cotton, killing weeds but not the cotton. Virtually all Georgia cotton grown now is Roundup Ready because it saves farmers time and money.

In 2004, rumors of resistant weeds started popping up. In 2005, it was confirmed: Georgia was the first place in the world to have glyphosate-resistant pigweed. Since then, it has been confirmed in 18 south-central Georgia counties. North Carolina, South Carolina, Tennessee and Arkansas have confirmed it, too.

Palmer amaranth pollen is dimpled much like a golf ball, which is designed to travel long distances, Sosnoskie said.

“Because Palmer amaranth is wind pollinated,” she said, “this trait has the potential to spread beyond a single farm or county. It’s not just one person’s problem. It’s everyone’s problem.”

Sosnoskie will take the information she collects (she already has two-year’s worth) and make mathematical models. The models can be used to show problem spots. Models can also show where it could spread and how.

The Georgia cotton industry must catch up and try to stay ahead of this growing issue, said Stanley Culpepper, a CAES weed specialist. He has compared the pigweed problem to the boll weevil. That little pest crippled cotton production in the Southeast in the mid-1900s. It continued to be a problem until a multimillion-dollar eradication program started in 1987 stopped the pest in 1994.

“This issue is not going away,” Culpepper said. “This research will be a key in helping get answers and provide growers and the industry ways to control its spread.”